I do have a set of Eminence Beta 12CX's kicking around but I doubt they will get me that low in a sealed cabinet...

See...I want to incorporate something into a tower build...open baffle tweeter...possibly an open baffle midbass driver or seal that too...

It rather depends.

For a while, I used a pair of 8" drivers in a sealed cabinet, and added ~14dB boost to get to 28Hz.
They weren't particularly high quality drivers (the 3mm Xmax was a giveaway in hindsight), but at reasonable-to-quite-loud levels, went plenty low enough.

They fell down when it came to movies played at movie levels: they bottomed out several times during the Dark Knight.
IMHO, for a compact sealed subwoofer, don't try to eq below 40Hz. Below that, excursion and power requirements become silly. 35Hz with a low Q (~0.5) would be okay, but add an infrasonic filter to stop the cones flapping around.

The PA drivers you mention won't be of much use here...

PA drivers are designed primarily for high output, with limited low end. They use lightweight cones and short-throw motors (where almost all the coil is in the magnetic gap, no overhang: efficiency improves but Xmax is small).
Remember at this point that most PA systems consist of a woofer and a tweeter in a smallish ported cabinet, driven by an amplifier. Below port tuning, the woofers unload (there's nothing holding the cones still, so they're free to flap around), and the operator perceives this as running out of bass.
No problem: turn up the low end on a graphic eq, tone controls, whatever.
So now you have a speaker that's mechanically unloaded, with excess LF power being fed into it to make up for the cabinet rolloff.

Any HiFi speaker would give up at this point and the voice coil would start smacking into various other parts of the speaker. PA speakers don't: they employ suspensions that are very non-linear.
A linear suspension means low distortion (perfect for HiFi), but of course if the user isn't careful, you risk mechanical damage. That's alright though - most HiFi speakers aren't pushed near their limits.
So, these non-linear suspensions mean, once the excursion starts, there's also increasing amounts of distortion. This is of little consequence to most people listening to the PA system as the sound will remain more-or-less intelligible (some people like the added harmonics, but that's irrelevant). Point is you'll never bottom them out, which will badly screw up the sound (and the audience will notice).

Thing is, if your subwoofer suddenly starts adding lots of harmonics to the sound, it'll immediately draw attention to itself, which is the opposite of what you want: subwoofers shouldn't noticably add to the sound, but you should be able to tell if someone switches it off.
The harmonics would also mean you'd be able to locate the subwoofer in the room. If the subwoofer's between the front two speakers, not so bad. If it's off to one side somewhere, you've got a problem.

Okay, so you need a dedicated (sub) woofer. If you're using two of them, decent 8"s will probably suffice, but if the 10"s aren't much more expensive, I'd be inclined to go with those.

So I figured if I could incorporate them into a tower build I would be a bit further ahead!!

Another thing...those subs are vented...what are the chances I could pull the drivers out and use them in a sealed cabinet??

If they're only needed to fill the sound out a little, 40Hz will be okay.

You could pull the drivers and put them in sealed cabinets. Ideally, you'd have the thiele-small parameters for them (perhaps you can get them measured?) so you can simulate and figure out the right specs for a Linkwitz Transform. You might find them okay without any LF boost, but there's no guarantee there. To get an idea of what you'll end up with, disconnect the internal amplifier, connect a different amplifier to the speaker (run the wire through the port) block up the ports (I use socks/scarves for this), and add something solid inside until the cabinet volume is ~20L. Have a listen. If you have some form of eq to hand (eg, Foobar2000), you could play with that until you're happy with the bass.

With some care, you could probably use the subwoofer plate amps too. Problem is that the manufacturer may have added eq in the plate amp for that driver in a ported box, so this would have to be bypassed or results would be unpredictable at best.